In conventional or “wet” lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with an aqueous medium, typically a fountain solution, and ink is applied, the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. Typically, the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
Imageable elements useful as lithographic printing plate precursors typically comprise an imageable layer applied over the hydrophilic surface of a substrate. The imageable layer includes one or more radiation-sensitive components, which may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material. Following imaging, either the imaged regions or the unimaged regions of the imageable layer are removed by a suitable developer, revealing the underlying hydrophilic surface of the substrate. If the imaged regions are removed, the precursor is positive-working. Conversely, if the unimaged regions are removed, the precursor is negative-working. In each instance, the regions of the imageable layer (i.e., the image areas) that remain are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water and aqueous solutions, typically a fountain solution, and repel ink.
The developers used to develop imaged imageable elements are typically aqueous alkaline solutions, which may contain substantial amounts of organic solvents. Disposal of substantial quantities of developer is expensive and can cause environmental problems. Thus, systems have been developed that do not require a developer.
Direct digital imaging, which obviates the need for imaging through a mask, is becoming increasingly important in the printing industry. Imageable systems for the preparation of lithographic printing plates have been developed for use with lasers. Burberry, U.S. Pat. No. 5,858,607, incorporated herein by reference, discloses an assemblage comprising a receptor with a hydrophilic surface, and a donor support comprising a layer of a cyanoacrylate polymer. These systems do not require a developer. When the assemblage is exposed with a high intensity laser beam, the cyanoacrylate polymer is transferred to the hydrophilic surface of the receptor to produce a lithographic printing plate.
In the preparation of these systems, the cyanoacrylate polymer is dissolved in a coating solvent and the resulting coating solution coated over the donor support to form the layer of the cyanoacrylate polymer. Typical coating solvents are acetonitrile, and halogenated organic solvents such as dichloromethane, chloroform, and methyl chloroform, which are toxic, and must be recovered in the coating operation. Thus, a need exists for a digitally imageable, processless imageable assemblage that does not require the use of toxic organic solvents in its preparation.